1. Technical Field of the Invention
The invention relates to a method and a system for altering the porosity of thin films, and more particularly, to a method and a system for creating a dielectric film having a low dielectric constant.
2. Description of Related Art
Microelectronic circuits perform a variety of functions in small designs. With growing circuit speeds and miniaturization, smaller circuit layouts stacked in a multilayer structure are susceptible to the parasitic effect of capacitive coupling.
One solution that controls the effect of capacitive coupling employs an interlayer dielectric having a low dielectric constant. The integration of low dielectric constant materials between integrated circuits isolate conductors, reduces power consumption, and lowers the parasitic effect of capacitive coupling.
Several materials can be used as dielectrics. One insulator used in microelectronic circuits is silicon dioxide (SiO2). Silicon dioxide has a dielectric constant of about four. One of the lowest known dielectric materials is air having a dielectric constant of about one. Unfortunately, air does not lend itself to multilayered design as it offers no underlying structure to support layered circuits.
Accordingly, there is a need for a method and a system that can achieve a low dielectric constant and also support multilayered circuits. One class of tunable dielectric constant materials having these properties is xerogels. Xerogels achieve a low dielectric constant through the integration of nanometer size pores within a silicon dioxide film. By applying a well-controlled evaporation process, the xerogels can achieve a tuned dielectric constant by tailoring the size and number of its pores. Xerogels can require strict atmospheric controls to achieve the desired pore size, pore distribution, and dielectric density. Accordingly, the preparation of xerogels can require considerable time.
In light of the above described problems, there is a need for a simple and timely method and system that creates a material having a predetermined dielectric constant that is capable of supporting the feature sizes of integrated circuits and lends itself to a multilayered design.
The invention provides a system and a method for densifying a surface of a porous film. By reducing the porosity of a film, the method yields a densified film that is more impenetrable to subsequent processes. The method comprises the steps of providing a film having an exposed surface. The film can be supported by a semiconductor substrate. When the film is moved to a processing position, a focused source of radiation is created by a beam source. The exposed surface of the film is then irradiated by the beam source at the processing position until a predetermined dielectric constant is achieved. The film or beam source may be rotated, inclined, and/or moved between a variety of positions to ensure that the exposed surface of the film is irradiated evenly.
Another aspect of this invention involves a system for fabricating a tuned dielectric film. The tuned dielectric fabricating system comprises a radiation source, a positioning device, and a controlling device. The radiation source emits a focused beam of radiation, which for example, may comprise an electron beam or ion implantation beam. The positioning device places the film at a location that can receive the focused beam of radiation. Preferably, the positioning device and radiation source are coupled to rotating and inclining devices. The controlling device can manipulate the radiation source, the positioning device, the rotating devices, and/or the inclining devices such that the focused beam of radiation irradiates the film until a predetermined dielectric constant is attained.
The radiation source may be rotated, inclined, and/or moved and may comprise a plurality of sources of radiation. The sources of radiation may irradiate select areas of the film from different positions to ensure even coverage. For example, where trenches are formed in the dielectric film, the plurality of radiation sources, which may be rotated, inclined, and/or positioned apart, will irradiate the sides and bottom of the trench uniformly. Adjacent surfaces can also be irradiated as can more than one trench.